The present invention relates to a non-volatile memory device and, more particularly, to a non-volatile memory devices including a plurality of common source lines in order to reduce a source line bouncing phenomenon.
In recent years, there is an increasing demand for non-volatile memory devices which can be programmed and erased electrically and do not require a refresh function of rewriting data at certain intervals.
A non-volatile memory device generally includes a memory cell array in which cells for storing data are arranged in a matrix form, and a page buffer for writing memory into specific cells of the memory cell array or reading memory stored in a specific cell. The page buffer includes a bit line pair connected to a specific memory cell, a register for temporarily storing data to be programmed into the memory cell array or reading data of a specific cell from the memory cell array and temporarily storing the read data, a sense node for sensing a voltage level of a specific bit line or a specific register, and a bit line selection unit for controlling whether to connect the specific bit line and the sense node.
To correctly determine whether a specific cell has been programmed, it is important to maintain sufficient read margin, if possible. In particular, each cell of a non-volatile memory device employing a Multi-Level Cell (MLC) programming method has various threshold voltage distributions compared with cells employing a Single Level Cell (SLC) programming method. Thus, without a sufficient sensing margin placed on distribution basis, source line bouncing phenomenon is unavoidable.
However, even though a program target cell has not been fully programmed at a verify reference voltage or more due to the bouncing phenomenon of a source line, which occurs according to the characteristic of a memory cell array, under-programmed cells that are verified to be fully programmed are generated. The sensing margin is further reduced due to the existence of the under-programmed cells.
This phenomenon becomes more severe as the resistance of a common source line is increased while the process size is reduced.